Explain Energy (is it physical)?

[voko]

Voko's answer looked like the following: Click to see

Nah, you dreamed incorrectly :)

The kinetic and potential energies are not deduced from a Hamiltonian or a Lagrangian. They are required to formulate those things to begin with, so they are "given" pretty much like forces are "given" in the Newtonian formalism.

And writing equations with energies is not really more complex than with forces, to put it mildly. The success of the Lagrangian mechanics is a solid confirmation.

 

[AlephZero]

A scale can have the pivot at the same level or even lower than the points where the pans are attached, and it can have a rigidly attached counter-weight below the pivot, so the entire rotating assembly is T-shaped. This will have stable equilibria within a range of mass deltas.

Fair enough, I hadn't thought about using a counterweight to provide a moment to counteract the instability.

But with my mindset of working in aerospace, a counterweight is just an extra part in the device and extra mass, and those are two good reasons for not having one if you can make a design that works without it.

(Of course a torsion spring would be lighter than a counterweight, and provide the same functionality)

 

[voko]

But with my mindset of working in aerospace, a counterweight is just an extra part in the device and extra mass, and those are two good reasons for not having one if you can make a design that works without it.

A have seen a few "chemist" style scales, and they had a tall stand, a dial at the bottom, and the pointing needle (more like a spear) all the way from the fulcrum to the dial. I think it doubled as a counterweight. I cannot say with certainty, however, that the fulcrum was "low" in them, so they could have been a combination design.

 

[AlephZero]

But interesting as this digression on scales may be, it doesn't change the point I was trying to make in my first post, which is that all these designs are just as easy to understand using "forces and moments" as using energy. Either way, you need to understand the kinematics of the machine to make a mathematical model of it.

 

[voko]

But interesting as this digression on scales may be, it doesn't change the point I was trying to make in my first post, which is that all these designs are just as easy to understand using "forces and moments" as using energy. Either way, you need to understand the kinematics of the machine to make a mathematical model of it.

I do not disagree. My idea that balance scales can be tricky was a result of quite a few discussions with somebody having a hard time with some particular variety of balance scales.

 

[Dale]

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